But analysts around the region debate whether the headlong rush might be driven more by a desire to consolidate power before a possible royal succession, desperation for cash to pay for his plans or simply unchecked ambition to put his stamp on the broader Middle East. And despite President Trump’s enthusiasm for the prince, some in the State Department, the Pentagon and the intelligence agencies say they fear that his impulsiveness could both set back his own goals and destabilize the region.
“He’s decided he doesn’t do anything cautiously,” said Philip Gordon, the White House Middle East coordinator under President Barack Obama. But, Mr. Gordon said, “if the crown prince alienates too many other princes and other pillars of the regime, pursues costly regional conflicts and scares off foreign investors, he could undermine the prospects for the very reforms he is trying to implement.”
The extrajudicial arrests have spooked investors enough, analysts say, to extinguish the prince’s plans for an public stock offering of Aramco, the Saudi state oil company, in New York or London next year. It had been a centerpiece of his overhaul.
The crown prince’s threats against Iran and Lebanon have raised the specter of wars that the Saudi military, already bogged down in Yemen, is ill-equipped to fight. Riyadh would be forced to depend on the United States or Israel in any new conflict.
His corruption purge at home, meanwhile, risks alienating parts of the royal family and the financial elite at a moment that would appear to demand unity, either to smooth a succession or to face off against Iran. As many as 17 people detained in the anti-corruption campaign have required medical treatment for abuse by their captors, according to a doctor from the nearest hospital and an American official tracking the situation.
The former Egyptian security chief, Habib el-Adli, said by one of his advisers and a former Egyptian interior minister to be advising Prince Mohammed, earned a reputation for brutality and torture under President Hosni Mubarak. His lawyers say he plans to appeal his recent sentence in absentia in Egypt to seven years in prison on charges of corruption.
Officials of the Saudi Royal Court referred press queries about these reports to the Embassy of the Kingdom of Saudi Arabia in Washington, where a spokeswoman, Fatimah Baeshen, said the embassy could not confirm or dispute them.
With the decline in the price of oil in recent years, Saudi Arabia has frozen projects and spent more than a third of its financial reserves, draining them to about $475 billion this fall from a peak of $737 billion in August 2014. At that burn rate, the kingdom has only a few years to lift its revenue or slash its spending to forestall a financial crisis.
Against that backdrop, the prince’s supporters argue that the anti-corruption campaign aims to recapture hundreds of billions of dollars that have leaked from the state budget through graft and self-dealing — money he needs to fund his development plans.
Prince Mohammed had appealed to the kingdom’s wealthy for months to invest in his modernization program. But some groused privately that his plans — like a new $500 billion business hub “for the dreamers of the world,” built from scratch and fueled entirely by clean energy — were ill-conceived and grandiose, and instead of investing at home they quietly moved their assets abroad.
Now, he is no longer merely asking. The Saudi government is pressing some of those detained and others still at large to sign over large sums in exchange for better treatment, according to an American official briefed on the crackdown and associates of the royal family Employees of some of those arrested had been summoned months before to answer questions about their bosses, a sign that the purge was planned well in advance.
A senior Saudi official defending the crackdown said this week that it was meant to show that the old rules of business in the kingdom had changed.
“Corruption is at every level, and there are hundreds of billions of riyals that are lost from the national economy every year,” the official said, speaking on the condition of anonymity to discuss sensitive government matters. “The point here was mainly to shock the system, to send a message that this will not be tolerated anymore and that nobody is immune.”
Corruption has been so endemic for so long — from inflated government contracts for large projects to simple bribes to obtain passports — that countless Saudis have participated. Yet, some princes with reputations for conspicuous corruption appear to have been left alone, raising questions about who is being targeted, and why.
Other signs suggest that Prince Mohammed may also be seeking to thwart perceived rivals. In June, he and his father stripped the titles of crown prince and interior minister from Prince Mohammed bin Nayef, 58, temporarily confining him to his palace. Admirers of the ousted crown prince were relieved last week when a video surfaced showing him moving freely through a family funeral, receiving kisses on his shoulder in a show of deference and loyalty from a procession of well-wishers.
That display of his continued popularity, however, may have been too much for the younger Prince Mohammed, who the next day ordered the seizure of the former crown prince’s assets, along with those of his wife and daughters, according to two family associates.
Ms. Baeshen, the Saudi embassy spokeswoman, said she could not comment on any potential investigations.
Some American officials suspect that Prince Mohammed may be rushing to lock down the levers of power in anticipation of a formal abdication by his father, King Salman, who scholars and Western officials say could be suffering from dementia.
When President Trump visited Riyadh for a summit meeting last summer, the king remained seated as he struggled to read a prepared statement. His speech was at times weak, halting or slurred. He seldom speaks publicly. Saudi officials, however, insist his mental capacities are sound.
Prince Mohammed’s supporters argue that Saudi Arabia’s recent threats against Iran and Lebanon came in response to provocations beyond his control. As he was preparing his anti-corruption roundup, they say, Tehran’s allies in Yemen launched an Iranian-made missile in the direction of Riyadh, where it was intercepted over the outskirts of the city. The Lebanese prime minister, Saad Hariri, resigned his position the same day with a televised speech from Riyadh that accused Iran and its Lebanese client Hezbollah of sowing “discord, devastation and destruction” in the region.
But many, including current and former American diplomats, say Prince Mohammed’s boldness also reflects his conviction that he has the support of Mr. Trump.
Even in the last days of the Obama administration, another Persian Gulf royal who had already forged deep ties around Washington, Crown Prince Mohammed bin Zayed al-Nahyan of Abu Dhabi began to promote his Saudi counterpart to the incoming Trump team as a useful ally. Both princes appear to have formed a particular bond with Jared Kushner, Mr. Trump’s son-in-law and adviser, who at 36 is a contemporary of the young Saudi prince.
Mr. Trump chose Saudi Arabia for the first foreign trip of his presidency, and Prince Mohammed and Mr. Kushner have built such a strong rapport that other American officials say they are not briefed on what the two discuss.
“Jared is a bit of a black hole,” said one State Department official, speaking on the condition of anonymity to discuss frustration with the White House. “There is no sense of the positions he has advocated. We can only guess, based on what he has done and where he has been.”
The official added: “The Emiratis and the Saudis have been very careful to cultivate him and bring him along” toward their “confrontational posture in the region.”
A White House official who also insisted on anonymity disputed the characterization of Mr. Kushner, saying he regularly briefed the State Department and National Security Council on his trips and conversations.
Mr. Kushner made his third visit to the kingdom this year — this time unannounced until his return to Washington — in late October, when American officials say he stayed up late talking with Prince Mohammed at his desert ranch. The sweep of arrests unfolded days later, and Mr. Trump was quick to applaud, although several White House officials said the Saudis gave Mr. Kushner no heads up on what was about to take place.
“I have great confidence in King Salman and the Crown Prince of Saudi Arabia, they know exactly what they are doing,” President Trump said on Twitter after the arrests had begun. “Some of those they are harshly treating have been ‘milking’ their country for years.”
Ms. Baeshen, the embassy spokeswoman, said that Saudi Arabia and the United States “enjoy a wide range of cooperative discussions” but that “domestic affairs are just that: domestic affairs.”
The State Department official, though, said that its diplomats, the Pentagon and the Central Intelligence Agency all felt “growing alarm” that Prince Mohammed “is behaving recklessly without sufficient consideration to the likely consequences of his behavior, and that has the potential to damage U.S. interests.”